1. Technical Field
The present invention relates to a technique for detecting a voltage of each battery cell with respect to an assembled battery in which a plurality of battery modules, each being formed by connecting a plurality of battery cells in series, are connected in series by a connection member.
2. Related Art
As disclosed in Japanese Unexamined Patent Publication No. 2010-9991, Japanese Unexamined Patent Publication No. 2000-199771, and Japanese Unexamined Patent Publication No. 2008-76339, for example, an assembled battery configured by connecting a plurality of battery modules, each configured by connecting a plurality of battery cells in series, in series is proposed. As disclosed in Japanese Unexamined Patent Publication No. 2010-9991, a connection member such as a bus bar, a lead wire, and the like is used for the connection of the battery modules. As disclosed in Japanese Unexamined Patent Publication No. 2012-220344, Japanese Unexamined Patent Publication No. 8-19188, and Japanese Unexamined Patent Publication No. 11-252809, an assembled battery configured by connecting a plurality of battery cells in series is also proposed.
A voltage detection terminal extends from each of both electrodes of the assembled battery and from between the battery cells. The ends of the voltage detection terminals are connected to the ends of voltage input terminals arranged in a voltage detection unit of a battery voltage detection device. The voltage detection unit measures a potential difference among the voltage detection terminals through the voltage input terminals, and detects the voltage of each battery cell based on the measurement result.
Japanese Unexamined Patent Publication No. 2000-199771, Japanese Unexamined Patent Publication No. 2008-76339, and Japanese Unexamined Patent Publication No. 2012-220344 disclose a battery voltage detection device for accurately detecting the voltage of each battery cell of the assembled battery.
In Japanese Unexamined Patent Publication No. 2000-199771, the voltage on both sides of each battery cell is divided with a resistance voltage dividing circuit, and then detected with the voltage detection unit. A reference potential of each battery module is transmitted to the voltage detection unit through a switch and a diode of the resistance voltage dividing circuit. Furthermore, the voltage that cancels out the voltage drop by the switch and the diode of the resistance voltage dividing circuit is indicated to the voltage detection unit by a switch and a diode of a compensation circuit.
In Japanese Unexamined Patent Publication No. 2008-76339, the battery modules are connected in series by a fuse. The voltage detection unit detects a voltage of a connecting point of the battery cells with respect to an intermediate reference point of one end of the fuse, and a voltage of a connecting point of the other end of the fuse with respect to the intermediate reference point and the battery module. A computation circuit computes the voltage of one or a plurality of battery cells and the voltage drop by the fuse based on the detection result of the voltage detection unit, and furthermore, corrects the voltage of the battery cell by the voltage drop by the fuse.
In Japanese Unexamined Patent Publication No. 2012-220344, the voltage measurement unit measures the voltage of each battery cell through the voltage detection terminal. A contact resistance calculation unit calculates a contact resistance generated at each voltage detection terminal. The voltage computation unit calculates the voltage of each battery cell using the measurement result of the voltage measurement unit and the calculation result of the contact resistance calculation unit.
The detected voltage of each battery cell is output to a controller and used to perform charging control, abnormality determination, and the like, as disclosed in Japanese Unexamined Patent Publication No. 8-19188 and Japanese Unexamined Patent Publication No. 11-252809.
In Japanese Unexamined Patent Publication No. 8-19188, a control device calculates a voltage difference of a minimum voltage and another voltage of the voltages of the battery cells, and starts or stops the charging with respect to each battery cell based on the result of comparing each voltage difference and a predetermined value.
In Japanese Unexamined Patent Publication No. 11-252809, the voltage of the assembled battery is also detected in addition to the voltage of each battery cell. Specifically, an assembled voltage detection circuit detects the voltage of the assembled battery through the voltage detection terminal connected to both electrodes of the assembled battery, and outputs the detection result to the control circuit. The control circuit calculates the sum of the voltages of the battery cells, and determines the presence or absence of abnormality based on the result of comparing the sum and the voltage of the assembled battery.
If a great number of battery modules are connected in series to configure the assembled battery, the capacity of the assembled battery becomes large but the number of battery cells and voltage detection terminals also increases. There is a limit to the number of voltage input terminals and the voltage detection performance in the voltage detection unit of one battery voltage detection device. Thus, if there are a great number of battery modules and battery cells configuring the assembled battery, the voltage of each battery cell cannot be detected with one battery voltage detection device.
The number of battery modules and battery cells configuring the assembled battery varies depending on the application of the assembled battery and the like. Thus, the number of voltage detection terminals in one or a plurality of designed battery modules may not match the number of voltage input terminals in the existing battery voltage detection device. If the battery voltage detection device is to be developed in such a case so that the number of terminals becomes the same for the one or the plurality of battery modules, the versatility lowers.
Furthermore, if the battery modules are connected by way of a connection member such as a bus bar, the voltage drop occurs when the current flows through the connection member. Thus, the voltage of each battery cell may not be accurately detected in the voltage detection unit.